Measurement of the electroweak production of a photon and a W boson in association with two jets in proton-proton collisions using the ATLAS Detector

This thesis presents the observation and cross section measurements for the electroweak production of a W boson and a photon associated with two high energy jets where the W boson decays to an electron or muon and its corresponding neutrino. The data analyzed consists of 140 fb$^{-1}$ of proton-proton collision data taken by the ATLAS detector between 2015 and 2018. A neural network is trained to separate the signal from the dominant sources of irreducible background. Backgrounds arising from misreconstructed objects are estimated using data driven approaches. A fit of the neural network output is then performed to extract the observed number of signal events. The physics process of interest is observed with a statistical significance of 9.0$\sigma$ which constitutes the first observation of this process using data collected by the ATLAS detector. The observed number of signal events is corrected for detector effects to obtain a total production fiducial cross section measurement of 15.8$\pm$3.0 fb, consistent with leading order Standard Model predictions. Differential cross section measurements as a function of 6 kinematic variables chosen for their potential sensitivity to new physics are also obtained. The differential cross section measurements are consistent with leading order Standard Model predictions.